Climate and moisture induced stresses in block-glued glulam members of timber bridges

perature and leads to moisture content (MC) variations across the cross section. The MC affects the physical and mechanical properties as well as the dimensions due to shrinkage and swelling below the fibre satura-tion point (FSP). Due to constrained volumetric strains, e.g. due to swelling and shrinkage, changes in moisture content impose moisture induced stresses (MIS) which, if exceeding the tensile strength perpen-dicular to the grain of the material, can cause fractures such as cracks or delaminations. Thus, the correct estimation of the MC is important for the design, quality assurance, and durability of timber bridges.
There was the question especially for large glulam members as produced by block-gluing about the impact of ambient climate variations on the moisture induced stresses and possible failure. Block glulam beams form wide cross-sections by gluing single glulam beams to each other. They are used as, e.g., main struc-tural elements for timber bridges, see Figure 1. Therefore, cross sections of practical dimensions were clas-sified regarding the assumed ambient climate in service by numerical simulations that showed the moisture content and gradient over the cross section. Finally, the moisture induced mechanical response was simu-lated using a coupled moisture diffusion and mechanical model. The results were summarized to a practical advice for the dimensioning.